Kidney dialysis has been a therapeutic boon to thousands of patients a year, who have severely compromised or nonexistent kidney function. However, many of these patients experience side effects and complications ranging from hypersensitivity to recurrent hypotension. For a general discussion of hemodialysis complications, see Levin, et al., "Complications During Dialysis", in Nissenson, et al., eds., Dialysis Therapy, Hanley & Belfes, Inc., 1986, p. 85. Among the most common of complications is hypotension, arising in 20-30 percent of all hemodialysis patients. Many of these patients experience chronic hypotension, some so severe that they cannot tolerate the procedure at all, and must resort to peritoneal dialysis or transplant. The incidence of intradialytic hypotension occurs most frequently in older patients and in women.
The cause of intradialytic hypotension varies depending on whether it occurs early or late in the treatment phase. It may result when the rate of intravascular volume depletion during ultrafiltration exceeds replacement. The diffusion of replacement fluid into the intravascular space counteracts the normal compensatory response of increased peripheral resistance. Also, hypotension can occur even during volume overload because of the time dependency of refilling of the intravascular space. Similarly, if the patient's weight is below the "dry weight", volume shifts may no longer be adequate to maintain blood pressure. For a discussion of the causes of hypotension in hemodialysis, see Schulman, et al., "Complications of Hemodialysis", in Principles and Practices of Nephrology, Jacobson, et al., eds., B. C. Decker, Inc., 1991, pp. 757-759.
Other causes of intradialytic hypotension have been described. Shulman, infra, p. 759 lists as early hemodialysis hypotension causes: dialyzer volume, bioincompatible membranes, various medications, sepsis, and pericardial tamponade; listed as late stage hypotension causes, in addition to ultrafiltration rate and a too low setting for dry weight: excessive weight gain, decline in osmolarity, acetate accumulation, arrhythmia, and autonomic neuropathy. It is significant to note that most of the common causes of intradialytic hypotension involve fluid volume changes for which the body is incapable of fully compensating.
Treatment of intradialytic hypotension focuses on its suspected cause. If a too rapid removal of fluids is the suspected cause, dialysis is discontinued and the patient is placed in the Trendelenburg position to enhance venous return. (See Kidney Electrolyte Disorders, eds. J. C. M. Chan, et al., Churchill Livingstone, 1990). The most common pharmacologic intervention for hypotension is administration of isotonic or hypertonic saline, to restore fluid balance. Pressor agents are not generally recommended, in part because a high percentage of hemodialysis patients are older persons with manifest clinical hypertension. In fact, it is recommended in designing hemodialysis regimens for these patients, that all blood pressure medication be curtailed for at least four hours prior to treatment.